Lots of thoughts this chapter. Next chapter is the final chapter of volume 2 so something big will happen.
I get the feeling this chapter hinted that Kurumi's friendship with Kokoro may have been fake from the beginning. It seems like Kurumi doesn't even remember how her and Kokoro first talked. And to add on to that, it seems Kurumi mostly ignored Kokoro even before Naoi showed up. Plus, all the current flashbacks from childhood are from Kokoro's unreliable POV, so it's possible young Kurumi took pity on a social outcast and then when her other friends quit talking to her, she used the fact that Kokoro was obsessed with her so that she wouldn't end up all alone.
Kokoro is questioning her choices, but still doesn't want to give up. It's starting to feel like sunk cost fallacy at this point. She pointed out all the ways that she doesn't think Kurumi's a good girlfriend. And it seems like the events of chapter 8 shook Kokoro's view of Kurumi. Before her narrative was that Naoi was forcing Kurumi to do bad things, but she saw Kurumi chase Naoi by her own choice and likely saw Kurumi stripping for Naoi by the pool with very little provocation. The desk reveal could be the final straw to break Kokoro's attachment to Kurumi. The flashback in chapter 7 showed that Kokoro was largely so fixated on Kurumi due to her perceived perfection and popularity, but if Kurumi's negative aspects are brought to light and she becomes a social outcast herself, what is left for Kokoro?
As for Naoi, she was hurt by Kurumi's words to her last chapter. She thinks she's been ditched. Her thoughts that Kurumi will self-destruct on her own feel like foreshadowing. But I don't believe she meant it when she said she didn't care. She's currently at the school too, but right now she's a wild card because there's no telling where she is exactly or how she'll respond to the situation. Though given this volume has softened up Naoi's personality, it's likely she'll choose to still help Kurumi in the end. Because I doubt the volume would end without her and Kurumi making up in some way.
Kurumi is also a wild card. Will she freeze up? Assault Isanuma? Flee the classroom? Try to jump from the school roof? The situation doesn't look good for her. It should be noted this particular cleaning day is the very last day before summer vacation, so something big will most likely go down and then the fallout will be dealt with without needing to worry about classes. So anything can happen.
Isanuma is the teacher's favorite student. And the teacher is currently upset with Kurumi anyway. Odds are the desk will be pinned on Kurumi even without proof. At which point the school will likely contact Kurumi's mother. And it likely won't be pretty, since this case was very public due to Isanuma throwing the desk into their classroom and doing a callout in front of all of their classmates, which will destroy Kurumi's reputation. Plus, Kurumi damaging school property. And as the one student pointed out, it would be deemed as Kurumi bullying Isanuma.